A lift-off shoe system for a tilt window, such as shown in U.S. Pat. No. 4,941,285, involves counterbalanced shoes that do not lock when a sash is tilted. Non-locking shoes rise to an equilibrium position when a sash is tilted, causing part of its weight to be removed from the counterbalanced shoes. Then sash pins can be lifted up out of shoe slots for removing a sash from a window.
Sash pins for non-locking, lift-off shoes pivot freely within shoe slots as a sash tilts and have heads that interlock with the shoe slots during normal operation. Removing a sash from the window requires tilting the sash out of the plane of the window to a position approximately normal to the plane of the window and then slanting the sash to lift an upper sash pin out of its shoe slot, followed by raising the remaining sash pin from its slot in the opposite shoe. Lift-off shoes can also be made to lock in place when a sash is tilted. Then a sash can be slanted as its sash pins are lifted clear of locked shoes.
Tilting a sash that is biased by non-locking, lift-off shoes reduces the sash weight supported by the shoes and allows them to rise under the force of counterbalance springs. Depending on the height of the sash when it is tilted, the sudden rising of the bottom of a tilted sash can surprise people inexperienced with this phenomenon. A person surprised by this may attempt to catch hold of the tilted sash and support its weight against possible accident, and this may lift the sash pins prematurely out of shoe slots and leave the sash unsupported.
I have devised a simple remedy that inhibits any premature or unintentional lifting of sash pins from shoe slots. My solution is easily integrated into all the existing types of lift-off sash shoes and can accomplish its safeguarding function very economically.